This invention relates to the stabilisation of material on moving conveyor surfaces, and particularly to a stabiliser unit for this purpose. It has especial application to sorting apparatus in which bulk material of relatively light specific weight is carried at speed along a conveyor to a sorting station where defective or rejected elements thereof are removed while the material is in free flight.
Where bulk material is to be transported on a conveyor belt at speed, upon delivery of the material to the belt it is subject to significant acceleration. This results in movement of the material on the conveyor and significant instability. While chutes or intermediate conveyor belts can be used to accelerate the material as it is delivered to the conveyor belt, it is not always possible to include a chute, and when the material is frozen or moist, chutes can be of limited use. While reference is made herein to conveyor belts, similar problems arise in the use of other conveyor surfaces, such as the peripheral surface of a rotating drum.
In the recognition that unstable material on a moving conveyor can create problems, various attempts have been made to provide an effective means by which such material can be stabilised. Soft rollers have been used, with the surface provided by foam or an airbag, but these have lead to some difficulties because the rollers were driven at least partly by contact with the material itself on the conveyor surface. In another proposal, a flexible open mesh is provided on a cylindrical surface mounted by a resilient core to a rotatable shaft. The shaft is rotated by a drive wheel on the shaft which engages the conveyer surface. Such a stabiliser is disclosed in U.S. Pat. No 4,830,180. While the use of a drive wheel to rebate the shaft reduces the demands on the surface contacting material on the conveyer, the downward force applied by the mesh to articles on the conveyer is essentially determined by the construction of the stabiliser. Thus, the stabilising material cannot be moved away from the conveyer, other than by contact with articles on the conveyer, without simultaneous removal of the drive wheel.